There are numerous types of downhole tools available. Some use slips to secure their position, which are in turn actuated by movement of a sleeve. Yet other tools perform different functions, such as opening and closing valves or ports responsive to the motion of the tool or hydraulic actuation of a piston. In the realm of hydraulically actuated tools in particular, pressure build-up inside or outside the tool was generally required. That pressure communicated through a wall of the tool into a sealed chamber. The actuating piston would form part of the sealed chamber such that the cavity would grow or shrink in volume as the piston moved responsive to the increase or decrease of hydraulic pressure within the tool. These variable-volume cavities outside the wall of the tool were sealed off with elastomeric O-rings or similar seals. These seals were subject to wear from contamination in wellbore fluids, stroking back and forth in normal operation, and/or temperature or chemical effects from the wellbore fluids. The concern that such sealing elements would wear out was that an open channel would be created through the lateral port in the wall of the tool from inside to outside of the tool, thus upsetting well operations and costing critically expensive downtime for the well operator.
The apparatus of the present invention was developed to address these concerns. The apparatus employs the principles of pressure differential but without fluid communication. Instead, the applied pressure differential creates a stress which allows the wall of the tool to flex preferably within its elastic limits. The flexing can then be employed to either create a signal which indirectly causes the tool to actuate, or to directly cause the tool to actuate by employing such techniques as hydrostatic pressure differentials.